Fuel reforming device

ABSTRACT

A fuel reforming device generates reformate gas containing a large amount of hydrogen by reforming a mixture of a hydrocarbon fuel and air, and supplies the reformate gas to a fuel cell stack ( 14 ). The fuel reforming device comprises a fuel injector ( 1 ) injecting the hydrocarbon fuel into a fuel mixing chamber ( 24 ), first and second air distribution valves ( 10, 11 ) supplying air to the fuel mixing chamber ( 24 ), and a reformer ( 5 ) which generates reformate gas by making the air-fuel mixture supplied from the fuel mixing chamber ( 24 ) react in the presence of a reforming catalyst. The reformer ( 5 ) is also provided with an oxidation catalyst. When the fuel reforming device starts operating, a large amount of air is supplied from the first and second air distribution valves ( 10, 11 ) to the fuel mixing chamber ( 24 ), and the oxidation catalyst in the reformer ( 5 ) promotes oxidation of the air-fuel mixture to warm up the reformer ( 5 ).

FIELD OF THE INVENTION

This invention relates to a reforming device which generates reformategas comprising mainly hydrogen from a hydrocarbon fuel.

BACKGROUND OF THE INVENTION

JP 2000-191304 published by Japanese Patent Office in 2000 discloses acatalytic combustor formed upstream of a reformer for starting ahydrocarbon fuel reforming device. The catalytic combustor is providedwith an electric heater. When the reforming device starts, the catalyticcombustor is first heated by the electric heater, and after preheatingis complete, fuel and air are supplied to the catalytic combustor andcatalyzed combustion is started. Combustion gas is supplied to thereformer and warms up the reformer.

After the reformer has warmed up, by supplying excess fuel to thecatalytic combustor, fuel vapor is generated, and the generated fuelvapor is supplied to the reformer to reform the fuel.

This catalytic combustor has therefore the functions of a heater whichheats the reformer, and a vaporizer which supplies fuel vapor to thereformer after warm-up.

SUMMARY OF THE INVENTION

If the reformer has not reached the activation temperature at which itcan start a reforming reaction when the catalytic combustor is ready tofunction as a vaporizer, fuel vapor supplied from the catalyticcombustor to the reformer is not reformed. In this case, the fuel vapormay be discharged into the air or heat may be taken from the reformerdue to condensation of the fuel vapor in the reformer.

In order to prevent this fault and to shorten the starting time requiredfor the reforming device, the catalyst in the reformer must be activatedwithout fail by the time the vaporizer starts supply of fuel vapor.

It is therefore an object of this invention to shorten the time requiredfor catalyst activation of the fuel reforming device. It is a furtherobject of this invention to smoothly shift from warm-up operation tonormal operation of the fuel reforming device.

In order to achieve the above object, this invention provides a fuelreforming device which generates reformate gas comprising hydrogen byreforming a mixture of a hydrocarbon fuel and air. The fuel reformingdevice comprises a fuel mixing chamber, a fuel injector which injectsthe hydrocarbon fuel into the fuel mixing chamber, a first airdistribution valve which supplies air to the fuel mixing chamber andgenerates an air-fuel mixture, a second air distribution valve whichfurther supplies air to the air-fuel mixture in the fuel mixing chamber,and a reformer comprising a reforming catalyst which generates reformategas by causing the air-fuel mixture supplied from the fuel mixingchamber to undergo reforming reaction, and an oxidation catalyst whichcauses the air-fuel mixture to undergo a catalytic combustion.

The details as well as other features and advantages of this inventionare set forth in the remainder of the specification and are shown in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a reforming device according to thisinvention.

FIG. 2 is a flowchart describing a warm-up routine of the fuel reformingdevice performed by a controller according to this invention.

FIG. 3 is a timing chart describing variations in the amount of fuel andair supplied to a reformer due to execution of the warm-up routine.

FIG. 4 is a flowchart describing a valve control subroutine performed bythe controller.

FIG. 5 is a flowchart describing a control routine of the reformingdevice during a load increase performed by the controller.

FIG. 6 is a flowchart describing a control routine of the reformingdevice during shut-down performed by the controller.

FIG. 7 is a flowchart describing a control routine of the reformingdevice during a load increase performed by a controller according to asecond embodiment of this invention.

FIG. 8 is a flowchart describing a control routine of the reformingdevice during a load increase performed by a controller according to athird embodiment of this invention.

FIG. 9 is a flowchart describing a control routine of the reformingdevice during shut-down performed by the controller according to afourth embodiment of this invention.

FIG. 10 is similar to FIG. 1 but showing a fifth embodiment of thisinvention.

FIG. 11 is similar to FIG. 1, but showing a sixth embodiment of thisinvention.

FIG. 12 is similar to FIG. 1, but showing a seventh embodiment of thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, a fuel mixing chamber 24, electricheater 4, reformer 5, heat exchanger 6, shift converter 7 andpreferential oxidation reactor (PROX reactor) 8 are arranged in orderinside a housing 20 of a fuel reforming device used for a fuel cellpower plant.

A fuel injector 1 is installed in the fuel mixing chamber 24. The fuelinjector 1 injects a hydrocarbon fuel such as gasoline or methanol intothe fuel mixing chamber 24 from a nozzle 1A.

A first air supply port 2 and second air supply port 3 which supply airto the injected fuel are provided in the fuel mixing chamber 24. The airis supplied from a blower 9 to the first air supply port 2 via an airsupply passage 22 and a first air distribution valve 10. The first airdistribution valve 10 makes the remaining air flow into the air supplypassage 21. The air supply flowrate of the first air supply port 2increases, the larger the opening of the first air distribution valve 10is.

Air is supplied from the air supply passage 21 to a second air supplyport 3 via a second air distribution valve 11. The supply flowrate ofthe second air supply port 3 increases, the larger the opening of thesecond d air distribution valve 11 is. This air mixes with the fuelspray from the fuel injector 1, and generates an air-fuel mixture in thefuel mixing chamber 24. The opening of the first air supply port 2 ispreferably near a nozzle 1A of the fuel injector 1 so that atomizationof fuel immediately after it is injected from the nozzle 1A, ispromoted. It is also possible to use a compressor instead of a blower 9.

After the air supply passage 21 shunts part of the air in the second airdistribution valve 11 to the second air supply port 3, it is connectedto a PROX reactor 8.

An air supply flowrate AFM1 to the first air distribution valve 10 isdetected by a first flowrate sensor 12, and an air supply flowrate AFM2to the second air distribution valve 11 is detected by a second flowratesensor 13, respectively.

The fuel-air mixture generated in the fuel mixing chamber 24 is heatedby the electric heater 4, and is sent to the reformer 5 in the gaseousstate. It is preferred to also make the heating element of the electricheater 4 support an oxidation catalyst which has a fuel reformingaction.

The reformer 5 contains both a reforming catalyst and an oxidationcatalyst, or contains a reforming catalyst having a combinedoxidation-catalyst function. It is known that the following three kindsof reforming reactions apply to the reforming of hydrocarbon fuel.

Specifically, these are vapor reforming, partial oxidation reforming,and autothermal reforming (ATR)).

Vapor reforming may be represented by the following equation (1).$\begin{matrix}{{{C_{m}H_{m}} + {m\quad H_{2}O}}->{{\left( {m + \frac{n}{2}} \right)H_{2}} + {m{CO}}}} & (1)\end{matrix}$

The reaction of equation (1) is accompanied by reactions shown by thefollowing equations (2) and (3).3H₂+CO→CH₄+H₂O  (2)2H₂+2CO→CH₄+CO₂  (3)

When the reforming atmosphere is at high temperature, the reaction ofequation (1) is mainly performed. Consequently, the concentration of thehydrogen and carbon oxide contained in the reformate gas increases. Thereaction of equation (1) is an endothermic reaction, and in order tomaintain the reaction, heat must be supplied.

When the reforming atmosphere is at low temperature, the reactionproportions of equations (2) and (3) increase, so the concentrations ofhydrogen and carbon monoxide in the reformate gas falls, and theconcentrations of methane and water vapor increase. Partial-oxidationreforming is represented by the following equation (4). $\begin{matrix}{{{C_{m}H_{n}} + {\frac{m\quad}{2}O_{2}}}->{{\frac{n}{2}H_{2}} + {m{CO}}}} & (4)\end{matrix}$

This reaction is an exothermic reaction, and can be maintained byadjusting the fuel vapor supply amount and air supply amount.

Autothermal reforming is a combination of vapor reforming andpartial-oxidation reforming which are performed at the same reactionsite, and heat exchange between endothermic reactions and exothermicreactions are balanced.

Although the partial oxidation reformer is applied to the reformer 5 ofthis reforming device, the reformer 5 may be of any type which performsa reforming reaction. Also, all reforming reactions takes place under arich fuel-air ratio where the fuel concentration is higher than thestoichiometric air fuel ratio.

A heat exchanger 6 is situated downstream of the reformer 5, andpreheats the air delivered by the blower 9 with the heat of reformategas.

The shift converter 7 located downstream of the heat exchanger 6 andPROX reactor 8 are known devices for removing the carbon monoxide (CO)contained in reformate gas. The shift converter 7 converts the carbonmonoxide in reformate gas into carbon dioxide (CO₂) using water, and thePROX reactor 8 converts the carbon monoxide in reformate gas into carbondioxide (CO₂) using the oxygen in the air supplied from the second airdistribution valve 11, respectively.

The operations of the fuel injector 1, the first air distribution valve10, the second air distribution valve 11, the blower 9, and the electricheater 4 are controlled by a controller 30.

Although only the fuel injector 1 is shown in FIG. 1 as a device whichperforms fuel injection, fuel is supplied to the fuel injector 1 at aconstant pressure from a fuel pump, not shown, and the fuel injector 1injects fuel according to a fuel injection signal from the controller30. The injection amount of the fuel injector 1 is controlled bycontrolling the valve-opening time period of the nozzle 1A using a pulsewidth modulation signal, or by adjusting the opening degree of thenozzle 1A.

The controller 30 comprises a microcomputer provided with a centralprocessing unit (CPU), read-only memory (ROM), random access memory(RAM) and input\output interface (I/O interface). The controller 30 mayalso comprise plural microcomputers.

To perform this control, the fuel reforming device comprises atemperature sensor 31 which detects the temperature of the electricheater 4, a temperature sensor 32 which detects the temperature of thereformer 5, a temperature sensor 33 which detects the temperature of thePROX reactor 8, a load sensor 34 which detects the power generation loadof the fuel cell power plant and a main switch 35 which switches thefuel cell power plant ON or OFF. The detection temperatures of thesetemperature sensors 31-35 are respectively input into the controller 30as signals.

Next, referring to FIG. 2, a warm-up routine of the fuel reformingdevice performed by the controller 30 will be described. This routine isperformed when the main switch 35 is turned ON.

First, the controller 30 energizes the electric heater 4 in a step S1.

In a following step S2, the temperature of the electric heater 4detected by the temperature sensor 31 is compared with a targettemperature T0. The target temperature T0 is a temperature fordetermining whether or not fuel supply has started. The controller 30stands by without proceeding to future steps until the temperature ofthe electric heater 4 reaches the target temperature T0. When thetemperature of the electric heater 4 reaches the target temperature T0,the controller 30 reads the temperature of the reformer 5 detected bythe temperature sensor 32 in a step S3, and stores it in an internal RAMas a temperature T1.

In a following step S4, fuel injection by the fuel injector 1 and theoperation of the blower 9 are started to supply fuel and air to the fuelmixing chamber 24.

When the step S4 is executed for the first time, the target fuelinjection amount and a target air supply amount are respectively set topredetermined values. The blower 9, once its operation starts, continuesits operation until the processing of a step 17 which will be describedlater is performed.

When the step S4 is executed for the second time or later, increase inthe target fuel injection amount and the target air supply amount aswell as the corresponding control of the fuel injector 1, the firstdistribution valve 10 and the second distribution valve 11 are performedrespectively applying predetermined increments. The distribution ratioof the first air distribution valve 10 is regulated so that the fuel-airmixture supplied to the reformer 5 is a lean air-fuel mixture having anair excess factor of 2 to 5. In the processing of the step S4 when it isperformed for the second time or later, the control of air supply amountis performed by first regulating the opening of the first airdistribution valve 10 and, when the air supply amount is still less thanthe target air supply amount after the regulation of the opening of thefirst air distribution valve 10, the opening of the second airdistribution valve 11 is then regulated.

A lean air-fuel mixture is supplied to the reformer 5 to perform acatalytic combustion of the air-fuel mixture in the presence of theoxidation catalyst in the reformer 5 to raise the temperature of thereforming catalyst in the reformer 5 as well as to warm up the heatexchanger 6, shift converter 7 and PROX reactor 8 by the heat of thecombustion gas.

In a following step S5, the controller 30 again reads the temperature ofthe reformer 5 detected by the temperature sensor 32, and stores it inthe internal RAM as a temperature T2.

In a following step S6, the temperature T2 is compared with a warm-uptarget temperature Ts of the reformer 5. When the temperature T2 hasreached the warm-up target temperature Ts, the controller 30 performsthe processing of steps S13-S17. When the temperature T2 has not reachedthe warm-up target temperature Ts, the controller 30 performs theprocessing of steps S7-S12. The warm-up target temperature Ts is thetemperature at which a partial oxidation reaction can occur in the leanair-fuel mixture, and is generally 200 to 500 degrees centigrade.

In a step S7, the temperature T2 is compared with the temperature T1before start of fuel supply which was stored in the RAM. When thetemperature T2 is lower than the temperature T1, the controller 30, in astep S8, substitutes the value of the temperature T2 for the temperatureT1, and repeats the processing from the step S5.

Thus, if the temperature T2 rises above the temperature T1 in the stepS7, the controller 30 stops energization of the electric heater 4 in thestep S9. The processing of the step S5-S8 means that heating by theelectric heater 4 is continued until the temperature of the reformer 5shows an increase after fuel supply has started. Also, in the step S7,the temperature rise confirms that heat of reaction has definitely beengenerated in the reformer 5.

Now, after energization of the electric heater 4 is stopped in the stepS9, the controller 30, in a step S10, compares a temperature differenceT2−T1 with a predetermined temperature difference ΔT0. The predeterminedtemperature difference ΔT0 is the target value of the temperature riseper unit time of the reformer 5. When the temperature difference T2−T1exceeds the predetermined temperature difference ΔT0, the catalyst ofthe reformer 5 may be damaged by thermal shock.

In this case, in a step S12, the controller 30 decreases the incrementfor the target fuel injection amount and the increment for the targetair supply amount which will be applied in the processing of the stepS4.

After the processing of the step S12, the controller 30, in a step S11,substitutes the value of the temperature T2 into the temperature T1, andrepeats the processing from the step S4. Also, in the step S10, when thetemperature difference T2−T1 does not exceed the predeterminedtemperature difference ΔT0, the controller 30 likewise substitutes thevalue of the temperature T2 into the temperature T1 in a step S8, andrepeats the processing from the step S5.

By repeating the processing of the steps S4-S12, when the temperature T2of the reformer 5 reaches the warm-up target temperature Ts in the stepS6, the controller 30 performs the processing of the steps S13-S17.

In the step S13, the controller 30 reads a temperature T3 of the PROXreactor 8 detected by the temperature sensor 33, and stores it in theinternal RAM.

In a following step S14, the controller 30 compares the temperature T3with a warm-up target temperature TSP of the PROX reactor 8. In general,the warm-up target temperature TSP of the PROX reactor 8 is 80-200degrees centigrade. Before the temperature T3 reaches the warm-up targettemperature TSP of the PROX reactor 8, the controller 30 does notproceed to future steps, but repeats reading of the temperature T3 ofthe step S13. Here, it is considered that the shift converter 7 situatedthe upstream has also reached warm-up temperature when the temperatureT3 of the PROX reactor 8 reaches the warm-up target temperature TSP.

When the temperature T3 reaches the warm-up target temperature TSP ofthe PROX reactor 8 in the step S14, the controller 30, in a step S15, byperforming a subroutine shown in FIG. 4 controls the opening of thefirst air distribution valve 10 and second air distribution valve 11 sothat the air supply amount of the first air supply port 2 is an airsupply amount corresponding to a rich air-fuel mixture where the airexcess factor lambda is 0.2 to 0.5, while the total air supply amount tothe reformer 5 including the supply air amount of the second air supplyport 3, is maintained at an air amount corresponding to a lean air-fuelmixture where the air excess factor lambda is 2 to 5.

In a step S16, by making the distribution ratio of the second airdistribution valve 11 to the second air supply port 3, zero, air supplyfrom the second air supply port 3 to the reformer 5 is interrupted, andthe fuel-air mixture in the reformer 5 is changed from a lean air-fuelmixture where the air excess factor lambda is 2 to 5, to a rich air-fuelmixture where the air excess factor lambda is 0.2 to 0.5.

In a final step S17, the controller 30 respectively controls therotation speed of the blower 9, the opening of the first airdistribution valve 10 and the second air distribution valve 11, to theiroptimum values for the normal operation of the reforming device. Afterthe processing of the step S17 the controller 30 terminates the routine.

Next, the valve control subroutine performed by the controller 30 in thestep S15 will be described referring to FIG. 4.

First, the controller 30 reads an air supply flowrate AFM1 to the firstair distribution valve 10 detected by the first flowrate sensor 12 in astep S101.

In a following step S102, the controller 30 stores the air supplyflowrate AFM1 to the first air distribution valve 10 as an initial valueAFM0 in the RAM.

In a following step S103, the controller 30 reads an air supply amountAFM2 to the second air distribution valve 11 detected by the secondflowrate sensor 13.

In a following step S104, the controller 30 subtracts AFM2 from AFM1 tocalculate the air supply flowrate of the first air supply port 2.

In a following step S105, it is determined whether or not the ratio ofthe fuel injection amount of the fuel injector 1 and the air supplyamount of the first air supply port 2, corresponds to a rich air-fuelmixture where the air excess factor lambda is 0.2 to 0.5. The fuelinjection amount of the fuel injector 1 is controlled by a signal fromthe controller 30, as mentioned above. Therefore, the fuel injectionamount of the fuel injector 1 is already known by the controller 30.

When the determination result of the step S105 is affirmative, thecontroller 30 terminates the subroutine.

In the step S4 of the routine of FIG. 2 performed prior to execution ofthis subroutine, a lean air-fuel mixture is generated in the reformer 5by increasing the distribution ratio from the first air distributionvalve 10 to the fuel mixing chamber 24. Therefore, when thedetermination result of the step S105 is negative, it means that the airsupply amount by the first air distribution valve 10 is excessive.

In a Step S106, the controller 30 increases the opening of the secondair distribution valve 11 by one step. In a step 107, the opening of thefirst air distribution valve 10 is decreased by one step. As a result ofthe processing of the steps S106, S107, the air supply flowrate of thefirst air supply port 2 decreases relatively to the air supply flowrateof the second air supply port 3.

In a following step S108, the controller 30 again reads the air supplyflowrate AFM1 to the first air distribution valve 10 detected by thefirst flowrate sensor 12.

In a following step S109, the controller 30 compares the air supplyflowrate AFM1 to the first air distribution valve 10 with the initialvalue AFM0 stored in the RAM.

When the air supply flowrate AFM1 to the first air distribution valve 10exceeds the initial value AFM0, i.e., when the air supply flowrate AFM1to the first air distribution valve 10 increases as a result of theprocessing of the steps S106, S107, the controller 30 again returns tothe step S107, and decreases the opening of the first air distributionvalve 10 by one step. If the opening of the first air distribution valve10 decreases, i.e., the distribution ratio to the first air supply port2 is decreased, the air flow rate of the air supply passage 21 isincreased, and the air flow resistance thereof will increase, so the airsupply flowrate AFM1 to the first air distribution valve 10 decreases asa result.

Also, if the opening of the second air distribution valve 11 isincreased, air flow resistance in the air supply passage 21 upstream ofthe second air distribution valve 11 will decrease, so the air supplyflowrate AFM1 to the first air distribution valve 10 increases as aresult.

When the processing of the steps S107-S109 is repeated, and the airsupply flowrate AFM1 to the first air distribution valve 10 reaches theinitial value AFM0 in the Step S109, the controller 30, in a Step S110,compares the absolute value of the difference of AFM1 and AFM0 with apredetermined variation ΔAFM. When the absolute value of the differenceof AFM1 and AFM0 is less than the variation ΔAFM, it shows that the airsupply flowrate AFM1 to the first air distribution valve 10 is stablenear the initial value AFM0. In this case, the controller 30 repeats theprocessing of the step S104 and subsequent steps. On the other hand, ifthe absolute value of the difference of AFM1 and AFM0 is not less thanthe variation ΔAFM in the Step S110, the controller 30 repeats theprocessing of the Steps S106-S110 until the absolute value of thedifference of AFM1 and AFM0 is less than the variation ΔAFM.

In other words, the processing of the steps S104-S110 decreases the airsupply flowrate of the first air supply port 2 and increases the airsupply flowrate of the second air supply port 3 without varying the airsupply flowrate AFM1 to the first air distribution valve 10.

In this way, in a step S105, when the air supply flowrate of the firstair supply port 2 is a flowrate corresponding to the aforesaid richair-fuel mixture where the air excess factor lambda is 0.2 to 0.5, thecontroller 30 terminates the subroutine.

Hence, when the fuel reforming device is started, the lean air-fuelmixture is first heated by the electric heater 4 and supplied to thereformer 5 such that the temperature of the reformer 5 is raised bygeneration of heat due to the oxidation of the lean air-fuel mixture.When the temperature of the reformer 5 begins to rise, the electricheater 4 is turned OFF, and the air supply amount to the reformer 5 isregulated so that the temperature of the reformer 5 does not rise toorapidly. When the temperature of the reformer 5 reaches the warm-uptarget temperature Ts and the temperature of the PROX reactor 8 reachesthe warm-up target temperature TSP, the lean air-fuel mixture which wassupplied to the reformer 5 is immediately changed over to the originalrich air-fuel mixture for reforming.

Thus, the catalyst can be activated in a short time using the reactionheat of oxidation of the lean air-fuel mixture in the reformer 5, whilemaintaining energization of the heater 4 at the minimum. After verifyingthat the catalyst temperature of the reformer 5 and the temperature ofthe PROX reactor 8 have reached the respective warm-up targettemperatures, a rich air-fuel mixture for reforming is supplied to thereformer 5. When this rich air-fuel mixture is supplied, the catalystsin the reformer 5 and PROX reactor 8 are activated without fail, and thetransition to normal running takes place without delay.

FIG. 3 shows the change of composition of the fuel-air mixture suppliedto the reformer 5 during execution of the warm-up routine. First, due tothe processing of the Step S4, a large amount of air is supplied fromthe first air supply port 2 to the fuel mixing chamber 24, and when thefuel injector 1 starts injection of fuel, a lean air-fuel mixture issupplied to the reformer 5. Further, insufficient air is supplied fromthe second air supply port 3 so that the air excess factor lambda of thelean air-fuel mixture is a target value in the range of 2-5.

During the processing of the Steps S5-S14, supply of this lean air-fuelmixture is maintained, and warm-up of the reformer 5, shift converter 7and PROX reactor 8 is continued. When warm-up of the PROX reactor 8 isconfirmed to be complete in the Step S14, the air supply amount of thefirst air supply port 2 is reduced to the supply amount in ordinaryreforming operation in the step S15, and by increasing the air supplyamount of the second air supply port 3, the same lean air-fuel mixtureis supplied to the reformer 5.

Then, by stopping the air supply by the second air supply port 3 in thestep S16, a change-over is made to a rich air-fuel mixture where the airexcess factor lambda is 0.2-0.5. Thereafter, ordinary reformingoperation is performed by the reformer 5, the shift converter 7, and thePROX reactor 8, all of which have completed warm-up.

The processing of the step S15 corresponds to preparation toinstantaneously change over the concentration of the fuel-air mixturefrom a lean air-fuel mixture to a rich air-fuel mixture. As a result ofthe processing of the step S15, when the air supply from the second airsupply port 3 to the reformer 5 is interrupted in the step S16, theconcentration of the fuel-air mixture immediately changes from a leanair-fuel mixture where the air excess factor lambda is 2 to 5, to a richair-fuel mixture where the air excess factor is 0.2 to 0.5.

When a fuel-air mixture near the stoichiometric air-fuel ratio issupplied to the reformer 5, the reaction temperature reaches a very hightemperature exceeding 2000 degrees centigrade, but by immediatelychanging from a lean air-fuel mixture to a rich air-fuel mixture in thisway, catalyst deterioration or dissolution of the catalyst support orthe reformer 5 due to a air-fuel mixture near the stoichiometricair-fuel ratio, can be prevented.

The change-over from a lean air-fuel mixture to a rich air-fuel mixtureis performed only by a valve operation, and there is no necessity tovary the air supply amount of the blower 9. In an ordinary rotating typeblower, there is an operation response delay, but as the lean air-fuelmixture is changed over to the rich air-fuel mixture only by a valveoperation, there is no response delay in the variation of theconcentration of the air-fuel mixture even if an ordinary rotating typeblower is used for the blower 9.

Also, at other times apart from change-over of the air-fuel mixture, asshown in FIG. 3, air is supplied mainly from the first air supply port 2near the fuel injector 1, so atomization of the fuel immediately afterinjection can be efficiently performed using the shear force of the airdischarged from the first air supply port 2.

Next, referring to FIG. 5, a routine for controlling the fuel reformingdevice performed by the controller 30 when this fuel reforming device isoperating normally and the power generation load of the fuel cell powerplant exceeds the normal load, will be described. This routine isexecuted when the controller 30 detects a load increase during normaloperation of the fuel reforming device.

First, the controller 30 calculates a load increase amount in a stepS21. In a following step S22, a fuel increase amount corresponding tothe load increase amount is calculated.

In a following step S23, the controller 30 calculates a latent heatamount required to vaporize the fuel increase amount.

In a following step S24, the electric heater 4 is energized so that aheat amount equivalent to the latent heat amount calculated in the stepS23, is generated. After the processing of the step S4, the controller30 terminates the routine.

The air supplied to the reformer 5 is heated by a heat exchanger 6before supply. Although the fuel injected by the fuel injector 1 isvaporized by the high temperature air supplied from the first air supplyport 2, the latent heat amount consumed by vaporization is proportionalto the fuel injection amount. Therefore, when the fuel injection amountincreases, the heat amount due to the high temperature air from thefirst air supply port 2 will be insufficient, and vaporization of fuelwill become difficult. Hence, when the fuel injection amount increases,a heat amount equivalent to the increased latent heat amount is suppliedby the electric heater 4. Although not shown in the flowchart, when thepower generation load decreases to the normal load, the controller 30stops energization of the electric heater 4.

When the fuel injection amount increases according to the powergeneration load, the heat amount required to vaporize the extra fuelimmediately after increase may temporarily exceed the heat amountobtained from the heat exchanger 6, but due to the above routine, evenin this case, the heat amount which could not be supplied by theelectric heater 4 is compensated, so there is no risk that unvaporizedfuel will be supplied to the reformer 5, and temporary decline in theperformance of the reformer 5 is prevented.

Next, referring to FIG. 6, a control routine performed by the controller30 when the operation of the fuel reforming device stops, will bedescribed. This routine is executed when the controller 30 detects thatthe main switch 35 has changed over from ON to OFF.

In a step S41, the controller 30 stops the injection of fuel by the fuelinjector 1.

In a following step S42, after increasing the air supply amount of theblower 9 for a predetermined time, the controller 30 stops operation ofthe blower 9.

Due to the execution of this routine, when the fuel reforming devicestops operation, there is an oxidizing atmosphere in the deviceincluding the reformer 5, and fuel remaining inside the device iscompletely oxidized. Therefore, there is no possibility that unburntfuel remaining in the device during shutdown or re-starting will bedischarged into the outside air, and the exhaust gas composition isalways maintained in a desirable state.

Next, referring to FIG. 7, a second embodiment of this invention will bedescribed.

This embodiment relates to the control when there is an increase inload. The controller 30 performs the routine of FIG. 7 instead of theroutine of FIG. 5 of the first embodiment. In this routine, stepsS25-S27 are provided instead of the step S24 of the routine of FIG. 5.The remaining details of the other steps are identical to those of theroutine of FIG. 5.

In the Step S25, the controller 30 calculates an additional fuel amountrequired for generating heat equivalent to the latent heat which wascalculated in the step S23, by catalytic combustion in the reformer 5.

In the following step S26, the controller 30 calculates an air increaseamount to realize the catalytic combustion of the fuel increase amountcalculated in the step S22 and the additional fuel amount calculated inthe step S25. In the last step S27, the controller 30 determines therotation speed of the blower 9 and the opening of the first airdistribution valve 10 according to the calculated air increase amount,and operates the blower 9 and the first air distribution valve 10accordingly. Further, it increases the target fuel injection amount ofthe fuel injector 1 according to the fuel increase amount calculated inthe step S22 and the additional fuel amount calculated in the step S25.

In the first embodiment, the heat amount equivalent to the latent heatamount of the increased fuel was made up by the heat generated by theelectric heater 4, but in this embodiment, heat amount insufficiency iscompensated by increasing the fuel supply amount and air supply amount.According to this method, the air heating amount can be increased by theheat exchanger 6 corresponding to the fuel increase amount without usingthe electric heater 4.

Next, referring to FIG. 8, a third embodiment of this invention will bedescribed.

This embodiment relates to control when there is a load increase. Thecontroller 30 performs a routine of FIG. 8 instead of the routine ofFIG. 7 of the second embodiment. In this routine, the processing ofsteps S28-S31 is performed after execution of the step S26 of theroutine of FIG. 7. The processing of the other steps is identical tothat of the routine of FIG. 7.

In the step S28, the temperature rise amount in the reformer 5 isestimated based on the increased amount of fuel and increased amount ofair in the previous steps S21-S26.

In the following step S29, the controller 30 calculates the equilibriumgeneration amount of carbon monoxide based on the estimated temperaturein the reformer 5, the fuel injection amount and the air supply amountdetermined in the step S21-S26.

In the following step S30, the controller 30 calculates the oxygenamount required to remove the generated carbon monoxide. In the laststep S31, the controller 30 regulates the rotation speed of the blower 9and the opening of the first air distribution valve 10 such that the airincrease amount calculated in the step S26 and the oxygen amountcalculated in the step S30 are additionally supplied. Further, itincreases the target fuel injection amount according to the fuelincrease amount calculated in the step S22 and the additional fuelamount calculated in the step S25.

The allowable concentration of carbon monoxide in the reformate gasdepends on a poisoning deterioration limiting value of the electrolytemembrane of the fuel cell used by the fuel cell power plant. In the stepS30, the required oxygen amount is calculated so that the carbonmonoxide concentration in the reformate gas is less than the poisoningdeterioration limiting value.

According to this embodiment, not only an enhanced performance of theheat exchanger 6 to deal with the increase of fuel injection amount, butalso the prevention of an increase in the generation of carbon monoxideaccompanied with the increase in the fuel injection amount by increasingthe air supply amount to the PROX reactor 8, are realized. Therefore,according to this embodiment, even when the power generation loadincreases, the carbon monoxide concentration in the reformate gas can bemaintained in a desirable range below the allowable limit.

Next, referring to FIG. 9, a fourth embodiment of this invention will bedescribed.

This embodiment relates to the control when the operation of the fuelreforming device is terminated. When the fuel cell power plant stopsoperation, the controller 30 performs the routine of FIG. 9 instead ofthe routine of FIG. 6 of the first embodiment. In this routine, a stepS43 is provided instead of the step S42 of the routine of FIG. 6.

In the step S43, the controller 30 maximizes the air supply amount ofthe blower 9, and energizes the electric heater 4. After allowing thisstate to continue for a predetermined time period, operation of theblower 9 and energization of the electric heater 4 are stopped.

According to this embodiment, the fuel remaining inside the device isheated by the electric heater 4, so the remaining fuel can be oxidizedwith greater certainty.

Next, referring to FIG. 10, a fifth embodiment of this invention will bedescribed.

This embodiment relates to the construction of the fuel cell powerplant, the fuel cell power plant comprising a fuel cell stack 14comprising a stack 14 of fuel cells which generate power according to anelectrochemical reaction between hydrogen supplied to an anode 14A, andoxygen supplied to a cathode 14B. The reformate gas generated by thefuel reforming device is supplied to the anode 14A via a reformate gassupply passage 17, and air is supplied to the cathode 14B from a blower15. Due to power generation by the fuel cell stack 14, anode effluentcontaining hydrogen is discharged from the anode 14A, and cathodeeffluent containing air is discharged from the cathode 14B. Afterburning these effluents in a combustor 16, they are discharged into theair.

In this embodiment, the air supply passage 21 is connected to thereformate gas supply passage 17 instead of connecting it to the PROXreactor 8 as in the case of the first embodiment.

Immediately after the fuel reforming device has shifted from warm-up toreforming operation, the reforming reaction is not stable, and carbonmonoxide and unburnt hydrocarbon fuel may flow into the reformate gassupply passage 17. As a result, the concentration of carbon monoxide inthe reformate gas may exceed the allowable limit. According to thisembodiment, however, the air supplied to the reformate gas supplypassage 17 from the air supply passage 21 dilutes the concentration ofcarbon monoxide in the reformate gas, so the deterioration of thecatalyst with which the anode 14A is provided is prevented.

Next, referring to FIG. 11, a sixth embodiment of this invention will bedescribed.

This embodiment relates to the construction of the fuel cell powerplant. In this embodiment, the air supply passage 21 is connected to thecombustor 16 instead of connecting the air supply passage 21 to thereformate gas supply passage 17 as in the fifth embodiment.

In this embodiment, reformate gas containing carbon monoxide and unburnthydrocarbon fuel produced immediately after the fuel reforming devicehas shifted from warm-up to reforming operation, is diluted by the airsupplied from the air supply passage 21, and discharged into the air ina completely oxidized state by burning in the combustor 16.

In this embodiment, as carbon monoxide and unburnt hydrocarbon fueltemporarily flow into the anode 14A of the fuel cell stack 14, the anode14A must be constructed from a material having high resistance to carbonmonoxide and unburnt hydrocarbon fuel.

Next, referring to FIG. 12, a seventh embodiment of this invention willbe described.

This embodiment relates to the construction of the fuel reformingdevice. A third air distribution valve 13 is provided midway in the airsupply passage 22 from the blower 9 to the heat exchanger 6, and abypass passage 23 branches off from the third air distribution valve 13.The bypass passage 23 bypasses the heat exchanger 6, and rejoins the airsupply passage 22 again between the heat exchanger 6 and the firstflowrate sensor 12. The remaining features of the construction of thefuel reforming device are identical to those of the first embodiment.

During normal operation, the heat exchanger 6 warms the air sent outfrom the blower 9, which is supplied to the fuel reforming device. Onthe other hand, when operation stops, the third air distribution valve13 is operated to supply all of the air from the blower 9 to the fuelreforming device via the bypass passage 23 without heating.

As a result, the fuel injector 1 is cooled by the cool air supplied fromthe first air supply port 2. After fuel remaining at the tip of the fuelinjector 1 is blown away by this air and undergoes reforming andoxidation in the reformer 5, it is discharged into the air. Therefore,worsening of the exhaust gas composition when operation of the fuelreforming device is stopped or re-started, can be prevented.

The contents of Tokugan 2002-180433, with a filing date of Jun. 20, 2002in Japan, are hereby incorporated by reference.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art, inlight of the above teachings.

For example, the processing for load increase or stopping of operationof the second-fourth embodiments can be combined with the fifthembodiment or sixth embodiment.

INDUSTRIAL FIELD OF APPLICATION

According to this invention, the warm-up time period of the fuelreforming device is shortened, so the invention has preferable effectswhen it is applied to the reforming device of a fuel cell power plantfor a vehicle.

1. A fuel reforming device which generates reformate gas comprisinghydrogen by reforming a mixture of a hydrocarbon fuel and air,comprising: a fuel mixing chamber; a fuel injector which injects thehydrocarbon fuel into the fuel mixing chamber; a first air distributionvalve which supplies air to the fuel mixing chamber and generates anair-fuel mixture; a second air distribution valve which further suppliesair to the air-fuel mixture in the fuel mixing chamber; and a reformercomprising a reforming catalyst which generates reformate gas by causingthe air-fuel mixture supplied from the fuel mixing chamber to undergoreforming reaction, and an oxidation catalyst which causes the air-fuelmixture to undergo a catalytic combustion.
 2. The fuel reforming deviceas defined in claim 1, wherein the fuel reforming device furthercomprises a heater which heats the fuel-air mixture, and a controllerfunctioning to control the heater to heat the fuel-air mixture when thefuel reforming device starts operation, and control an air supply amountof the first air distribution valve to the fuel mixing chamber tomaintain an excess air factor of the air-fuel mixture in a predeterminedlean state.
 3. The fuel reforming device as defined in claim 2, whereinthe fuel reforming device further comprises a sensor which detects atemperature of the reformer, and the controller further functions todetermine whether or not the temperature of the reformer is ascending ina state where the air-fuel mixture heated by the heater is supplied tothe reformer, and when the temperature of the reformer is ascending,control the heater to stop heating the air-fuel mixture.
 4. The fuelreforming device as defined in claim 3, wherein the controller furtherfunctions to determine whether or not the temperature of the reformer isless than a predetermined temperature, to increase a fuel injectionamount of the fuel injector with a preset increment, to increase the airsupply amount with a preset increment, to determine whether or not anascending rate of the temperature of the reformer exceeds apredetermined rate in a state where the temperature of the reformer isless than the predetermined temperature, and when the ascending rateexceeds the predetermined rate, and to decrease the increment of thefuel injection amount and the increment of the air supply amount.
 5. Thefuel reforming device as defined in claim 4, wherein the controllerfurther functions, when the temperature of the reformer is not less thanthe predetermined temperature, to decrease the air supply amount of thefirst air distribution valve until the air excess factor of the air-fuelmixture reaches a predetermined rich state, increase the air supplyamount of the second air distribution valve to the fuel mixing chamberso as to compensate for the decrease of the air supply amount of thefirst air distribution valve, and then close the second air distributionvalve.
 6. The fuel reforming device as defined in claim 1, wherein thefuel reforming device further comprises an air supply mechanism whichsupplies air to the first air distribution valve and the second airdistribution valve, and a heat exchanger which heats the air between theair supply mechanism and the first air distribution valve by performingheat exchange between the air and a gas discharged from the reformer. 7.The fuel reforming device as defined in claim 1, wherein the fuelreforming device further comprises an air supply mechanism whichsupplies air to the first air distribution valve, and a carbon monoxideremoval device which removes carbon monoxide from the reformate gas by acatalytic reaction using air, the first air distribution valve isconfigured to bifurcate the air supplied from the air supply mechanismto the fuel mixing chamber and the second air distribution valve, andthe second air distribution valve is configured to bifurcate airsupplied from the first air distribution valve to the fuel mixingchamber and to the carbon monoxide removal device.
 8. The fuel reformingdevice as defined in claim 1, wherein the fuel reforming device is usedtogether with a fuel cell stack comprising an anode and a cathode, andgenerating power by an electrochemical reaction between hydrogen in thereformate gas supplied to the anode and oxygen supplied to the cathode,the fuel reforming device comprises an air supply mechanism whichsupplies air to the first air distribution valve, the first airdistribution valve is configured to bifurcate the air supplied from theair supply mechanism to the fuel mixing chamber and the second airdistribution valve, and the second air distribution valve is configuredto bifurcate the air supplied from the first air distribution valve tothe fuel mixing chamber and the anode.
 9. The fuel reforming device asdefined in claim 1, wherein the fuel reforming device is used togetherwith a fuel cell stack, comprising an anode and a cathode, andgenerating power by the electrochemical reaction between hydrogen in thereformate gas supplied to the anode and oxygen supplied to the cathode,and a combustor which burns an anode effluent discharged from the anode,the fuel reforming device comprises an air supply mechanism whichsupplies air to the first air distribution valve, the first airdistribution valve is configured to bifurcate the air supplied from theair supply mechanism to the fuel mixing chamber and the second airdistribution valve, and the second air distribution valve is configuredto bifurcate the air supplied from the first air distribution valve tothe fuel mixing chamber and the combustor.
 10. The fuel reforming deviceas defined in claim 1, wherein the fuel reforming device is usedtogether with a fuel cell stack which generates electric power accordingto a power generation load using hydrogen in the reformats gas suppliedby the fuel reforming device, and the fuel reforming device furthercomprises a heater which heats the air-fuel mixture, a sensor whichdetects the power generation load, and a controller functioning tocalculate an increase amount of hydrocarbon fuel corresponding to anincrease amount of the power generation load, to calculate a latent heatamount for vaporizing the increase amount of hydrocarbon fuel, and tocontrol the heater to heat the air-fuel mixture for compensating thelatent heat amount.
 11. The fuel reforming device as defined in claim 1,wherein the fuel reforming device is used together with a fuel cellstack which generates electric power according to a power generationload using hydrogen in the reformate gas supplied by the fuel reformingdevice, and the fuel reforming device further comprises an air supplymechanism which supplies air to the first air distribution valve, asensor which detects the power generation load, and a controllerfunctioning to calculate a first increase amount of hydrocarbon fuelcorresponding to an increase amount of the power generation load, tocalculate a latent heat amount for vaporizing the first increase amountof hydrocarbon fuel, to calculate a second increase amount ofhydrocarbon fuel for compensating the latent heat amount by a catalyticcombustion of the second increase amount of hydrocarbon fuel, toincrease a fuel injection amount of the fuel injector according to thesum of the first increase amount of hydrocarbon fuel and the secondincrease amount of hydrocarbon fuel, and to control the air supplymechanism and the first air distribution valve to increase an air supplyamount to the fuel mixing chamber according to an increased fuelinjection amount by the fuel injector.
 12. The fuel reforming device asdefined in claim 11, wherein the fuel reforming device further comprisesa carbon monoxide removal device which removes carbon monoxide from thereformate gas by a catalytic reaction using air, the first airdistribution valve is configured to bifurcate the air supplied from theair supply mechanism to the fuel mixing chamber and the second airdistribution valve, the second air distribution valve is configured tobifurcate air supplied from the first distribution valve to the fuelmixing chamber and the carbon monoxide removal device, and thecontroller further functions to estimate a temperature ascending amountof the reformer from the increased fuel injection amount by the fuelinjector and an increased air supply amount to the fuel mixing chamber,to calculate a generated amount of carbon monoxide in the reformercorresponding to the increased fuel injection amount and the increasedair supply amount, and to control the air supply mechanism and thesecond air distribution valve to supply a required amount of air to thecarbon monoxide removal device which the carbon monoxide removal devicerequires for removing carbon monoxide of the generated amount from thereformate gas.
 13. The fuel reforming device as defined in claim 1,wherein the fuel reforming device further comprises a switch whichcommands the fuel reforming device to start and stop operation, an airsupply mechanism which supplies air to the first air distribution valve,and a controller functioning, when the switch has commanded thereforming device to stop operation, to stop injection of hydrocarbonfuel by the fuel injector, and to maximize an air supply amount of theair supply mechanism.
 14. The fuel reforming device as defined in claim1, wherein the fuel reforming device further comprises a switch whichcommands the fuel reforming device to start and stop operation, an airsupply mechanism which supplies air to the first air distribution valve,a heater which heats the air-fuel mixture, and a controller functioning,when the switch has commanded the fuel reforming device to stopoperation, to stop injection of hydrocarbon fuel by the fuel injector,to maximize an air supply amount of the air supply mechanism, and toactivate the heater to heat the air-fuel mixture.
 15. The fuel reformingdevice as defined in claim 1, wherein the fuel reforming device furthercomprises an air supply mechanism which supplies air to the first airdistribution valve, a heat exchanger which warms an air supplied by theair supply mechanism to the first air distribution valve by heatexchange with the reformate gas, and a bypass passage which connects theair supply mechanism with the first air distribution valve bypassing theheat exchanger.